Process for preparing alkylidene-substituted-1, 4-dions derivatives

ABSTRACT

A process for the preparation of an monoalkylidene substituted 1,4-dions derivatives of formula (Ia) or (Ib) or a mixture of (Ia) and (Ib): wherein: R 1 , R 2  and R 3 , equal to or different from each other, are hydrogen atoms or C 1 -C 20  hydrocarbon groups: T 1  and T 2 , equal to or different from each other, are OR 4 . R 4 , NR 4   2 , SR 4  or PR 4   2 ; or T 1  and T 2  can be fused in an oxygen atom or a NR 4  group; said process comprises the step of reacting a compound of formula (II), with a compound of formula (IIIa) or (IIIb), in the presence of at least one equivalent with respect to the compound of formula (IIIa) or (IIIb) of a salts of a base or a neutral base at a temperature higher than  70 ° C.

The present invention relates to a novel process for preparing 1,4 dions derivatives substituted with alkylidene groups. These compounds are easily convertible into the corresponding alkyl-substituted derivatives that are used as electron donor compounds in the preparation of Ziegler-Natta heterogeneous catalysts for the polymerization of olefins.

Transformation of the alkylidene-substituted 1,4 dions derivatives into the matching alkyl-substituted compounds is normally a clean reaction with an almost quantitative yield. Therefore, in order to industrially produce these compounds in an industrially exploitable way, it is necessary to have an economically advantageous process for the production of the corresponding alkylidene-substituted compounds. By the term “economically advantageous” it is meant a process able to give the target product in good yields and acceptable purity by the use of such reagents and conditions that the process is as smooth and cheap as possible. Monoalkylidene-substituted succinic acid esters are known in the art for example by the article from C. G. Overberg, C. W. Roberts, J. Am. Chem. Soc., Vol. 71, pp. 3618-3621, 1949. This document describes the preparation of several types of 2-alkylidene-substituted succinic acid esters carrying out the Stobbe reaction using potassium tert-butoxide as a base and tert-butanol as a solvent. The starting diethyl succinate was used in excess with respect to both the starting ketone (25%) and the base, which in turn was in excess (about 10%) with respect to the ketone. The highest yields were obtained using acetone as a ketone and were 92% with respect to the ketone, but much lower with respect to the succinate (76%). Most importantly however, a long and complicate work-up (solvent distillation, acidification with diluted HCl to pH=3, complete solvent distillation, extraction with ether, extraction of the ethereal solution with basic water, acidification of basic water with HCl conc., extraction with ether, anhydrification, solvent evaporation) of the reaction was needed in order to separate the non-reacted reagents from the final product. This clearly would make such process very costly if carried out on a large scale.

More recently, EP 760,355 disclosed the preparation of a 2-alkylidene-substituted succinate via the Stobbe reaction and using cycloheptanone as starting ketone. The base was potassium tert-butoxide and the solvent was dimethylformamide (DMF). Again, the yields were high with respect to the ketone (97%) but lower with respect to the succinate (75%), which was used in excess (34%). Taking also into account the excess of base used it is possible to understand that also in this case the work-up of the reaction in order to obtain1 only the desired product would be troublesome on a large scale.

In J. Am. Chem Soc., Vol. 70, pp. 3571-3576, 1948 Kloetzel proposed a different approach for the preparation of 2-alkylidene-substituted succinates. The process comprises the reaction of fumaric acid ester with nitroalkane in the presence of diethylamine. While the yields were acceptable, the reaction required a very long time, 14-18 days, the starting nitroalkane was used in large excess (300%) with respect to the fumaric acid ester, and the isolation of the product was complicated due to the presence of N-nitrosodiethylamine, a highly hazardous compound, and nitroalkylsuccinic acid ester, not fully utilised reaction intermediate.

In Tetrahedron, Vol. 51, no. 14, pp. 4213-4222, 1995 Ballini used 1,8-diazabiciclo[5.4.0]undec-7-ene (DBU) as a base for a similar reaction of maleic acid ester with nitroalkane to obtain 2-alkylidene-substituted succinates. More recently, in Eur. J. Org. Chem., pp. 2927-2931, 2000, Ballini expanded the scope of this reaction to include also preparation of 2-alkylidene-substituted 4-oxo-butanoates and 1,4-diketones by the DBU-promoted reaction of nitroalkanes with the corresponding 2-en-1,4-dions. According to these documents the reaction times are quite short and the yields of the corresponding 2-alkylidene-1,4-dions (succinates, 4-oxo-butanoates and 1,4-diketones) are quite high. However the results of this reaction can be improved in terms of both yield and purity of the final product. In Tetrahedron Letters, Vol. 35, no. 49, pp. 9247-9250, 1994 Ballini tried also other bases such as basic alumina, Amberlyst A21 and triethylamine but he stated that the best reactant was DBU. In all these documents the reactions are carried oout at room temperature and no suggestion about a possible temperature effect in terms of yields is given.

Thus there is a need to find a process for preparing in high yields and in a simple and cheap way 2-alkylidene-substituted-1,4-dions derivatives.

The applicant has now discovered that such a desired process is feasible when the reaction between nitroalkane and 2-en-1,4-dions is carried out at high temperature.

It is therefore an object of the present invention a process for the preparation of 2-alkylidene-1,4-dions, derivatives, of formula (Ia) or (Ib) or a mixture of (Ia) and (Ib):

wherein:

-   R¹, R² and R³, equal to or different from each other, are hydrogen     atoms or C₁-C₂₀ hydrocarbon groups; optionally containing     heteroatoms belonging to group 13-17 of the periodic table; or R¹     and R² can join together to form a saturated or unsaturated C₃-C₁₀     ring optionally containing heteroatoms belonging to group 13-17 of     the periodic table; with the proviso that when R¹ and R² are both     hydrogen atoms, only compounds of formula (Ia) are obtained; -   preferably R³ is a hydrogen atom, a linear or branched, saturated or     unsaturated C₁-C₁₅ alkyl, C₃-C₁₀ cycloalkyl, C₆-C₁₀ aryl, C₇-C₁₂     alkylaryl or C₇-C₁₂ arylalkyl radical; more preferably R³ is a     hydrogen atom, a linear or secondary C₁-C₈ alkyl or C₅-C₇ cycloalkyl     group such as methyl, ethyl, isobutyl or cyclohexyl; even more     preferably R³ is a hydrogen atom; -   T¹ and T², equal to or different from each other, are H, OR⁴, R⁴,     NR⁴ ₂, SR⁴ or PR⁴ ₂; or T¹ and T² can be fused in an oxygen atom or     a NR⁴ group to form for example compounds of formula (Ic) or (Id):     and the corresponding double bonds isomers; -   R⁴, equal to or different from each other, are a C₁-C₂₀ hydrocarbon     group, optionally containing one or more heteroatoms belonging to     group 13-17 of the periodic table; -   preferably R⁴ is a linear or branched C₁-C₂₀ alkyl, C₃-C₁₀     cycloalkyl, C₆-C₁₀ aryl or a C₇-C₁₂ alkylaryl group; more preferably     R⁴ is a linear or branched C₁-C₈ alkyl or C₅-C₁₀ cycloalkyl group     such as methyl, ethyl, isobutyl, tert-butyl or cyclohexyl; -   preferably T¹ and T² are OR⁴, R⁴, NR⁴ ₂, SR⁴; more preferably T¹ and     T² are OR⁴; -   said process comprises the step of reacting a compound of formula     (II)     with a compound of formula (IIIa) or (IIIb)     in the presence of at least one equivalent with respect to the     compound of formula (IIIa) or (IIIb) of a salts of a base or a     neutral base at a temperature higher than 70° C.

For the purpose of the present invention “one equivalent” means the same amount of basic functionality i.e. the capability to accept an acidic proton. Thus for example one equivalent of K₂CO₃ means that only 0.5 mole of K₂CO₃ per mole of compound of formula (IIIa) or (IIIb) are used, for the reason that the anion CO₃ ²⁻ is able to accept 2 acidic protons. In the same way, for example, one equivalent of KHCO₃ means that one mole of KHCO₃ is used per one mole of compound of formula (IIIa) or (IIIb) for the reason that the anion HCO₃ ⁻ is able to accept one acidic proton.

Non limitative examples of a salts of a base or a neutral base are:

-   -   (i) oxides of metal if group 1-13 of the periodic table,         preferably from groups 1, 2 and 13; such as CaO, BaO and Al₂O₃;     -   (ii) compounds of formula NR⁹ ₃ wherein R⁹ equal to or different         from each other, are hydrogen atom, or a linear or branched,         saturated or unsaturated, C₁-C₁₀ allyl, C₆-C₂₀ aryl, C₇-C₂₀         arylalkyl or C₇-C₂₀ alkylaryl groups, optionally containing O,         S, N, P, Si or halogen atoms, or two or more R⁹ form one or more         saturated or unsaturated 4 to 7 membered rings, optionally         containing O, S, N, P or Si atoms, that can bear substituents;         when this ring is aromatic one R⁹ can also be a bond part of a         double bond to form for example compound like pyridine, or         pyrazine; preferably R⁹ is a linear or branched, saturated or         unsaturated, C₁-C₁₀ alkyl group or two R⁹ form a 5 or 6 membered         ring such as pyrrole, or the compound of formula NR⁹ ₃ is of         1,8-diazabiciclo[5.4.0]undec-7-ene (DBU);     -   (iii) compounds of formula MT_(j) wherein M is a metal of groups         1-12 of the periodic table, or a group NR⁹ ₄ ⁺ wherein R⁹ as         been described above, preferably M is a metal of groups 1, 2 of         the periodic table, more preferably M is sodium or potassium; T         is H, F⁻, OH⁻, HCO3⁻; RO⁻ or RC(O)O⁻ wherein R is a linear or         branched, saturated or unsaturated C₁-C₂₀-alkyl,         C₃-C₂₀-cycloalkyl, C₆-C₂₀-aryl, C₇-C₂₀-alkylaryl or         C₇-C₂₀-arylalkyl radical, optionally containing one or more         halogen atoms; j is equal to the valence of the metal M or 1 in         the case M is NR⁹ ₄ ⁺;     -   (iv) carbonates of metal M wherein M is a metal of groups 1-12         of the periodic table, preferably M is a metal of groups 1, 2 of         the periodic table, more preferably M is sodium or potassium.

Preferred salts are K₂CO₃; KHCO₃; Na₂CO₃; NaHCO₃;

Example of salts of a base or, neutral base salts that can be used in the present invention are:

-   Li₂CO₃; K₂CO₃; Na₂CO₃; MgCO₃; CaCO₃, BaCO₃; -   LiHCO3; KHCO₃; NaHCO₃; Mg(HCO₃)₂; Ca(HCO₃)₂, Ba(HCO₃)₂; -   LiOCH₃; KOCH₃; NaOCH₃; LiOCH₂CH₃; KOCH₂CH₃; NaOCH₂CH₃; -   LiOC(O)CH₃; KOC(O)CH₃; NaOC(O)CH₃; LiOC(O)CH₂CH₃; KOC(O)CH₂CH₃; -   NaOC(O)CH₂CH₃; NaOH; KOH; CH₃ONa; CH₃OK; CaO; BaO; LH; NaH;     (CH₃CH₂)₃N; NH₃.

The amount of the salt of a base or of the neutral base to be used in the process is at least one equivalent with respect to the compound of formula (IIIa) or (IIIb). Preferably the amount is between 1 and 4 equivalents, more preferably between 1 and 1.5.

Generally the molar ratio between the compounds of formula (II) and (IIIa) or (IIIb) ranges from 5 to 0.2, preferably from 1.5 to 0.5, more preferably from 1.2 to 1.

The reaction can be carried out both in protic and aprotic solvent, such as water, or alcohols for protic solvents and toluene, ethylbenzene, xylene, dimethylformammide (DMF), N,N-dimethylacetamide, 1-methyl-2-pyrrolidone, diethylether, tetrahydrofurane, acetonitrile, for aprotic solvents. As a general rule solvent having higher boiling point are preferred.

Otherwise the reaction can also be carried out without solvents when one or more reactants are in liquid phase.

As it has been explained, the above process is very suitable for obtaining the 2-alkylidene substituted-1,4-diones derivatives in very high yields. Moreover, the applicant found that by carrying out the process according to the above-mentioned conditions the work-up of the final reaction mixtures is very simple. In fact, in most of the cases the work-up comprises only a dilution of the reaction mixture with water and an extraction of the desired products with an appropriate organic solvent, which is then suitably removed.

One class of preferred compounds among those of formulas (Ia) or (Ib) is that in which R² is hydrogen and R¹ is selected from C₄-C₂₀ hydrocarbon groups. Among them, particularly preferred are the compounds in which R¹ is C₁-C₈ alkyl, C₅-C₁₀ cycloalkyl, C₆-C₁₀ aryl, C₇-C₁₂ alkylaryl or C₇-C₁₂ arylalkyl radical; even more preferred are the compounds in which R¹ is C₁-C₈ alkyl or C₅-C₁₀ cycloalkyl radical.

Another class of preferred compounds among those of formulas (Ia) or (Ib) is that in which both R¹ and R² are C₁-C₂₀ hydrocarbon groups, among them particularly preferred are the compounds in which R¹ and R², equal to or different from each other, are C₁-C₈ alkyl.

Examples of R¹ and R² are: methyl, ethyl, n-propyl, cyclobutyl, but-3-enyl, cyclopropyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, 1-ethylpropyl, cyclohexyl, 4methylcyclohexyl, 2-methylcyclohexyl, 3-methylcyclohexyl, neo-pentyl, cyclopentyl.

The compounds in which both R¹ and R² are the same and chosen among methyl, ethyl or propyl are preferred. Also preferred are the compounds in which R¹ and R² are linked together to form a cycle containing from 3 to 10 carbon atoms such as cyclopentyl, cyclohexyl, or cycloheptyl.

In carrying out the process of the present invention the reactants can be brought into contact with each other according to any order whatsoever.

The temperature for carrying out the process ranges from 70 to 300° C., more typically from 80 to 220° C. and preferably from 150 to 200° C. The skilled in the art can easily select, within these ranges, the optimum temperature by taking into account parameters like the boiling temperature of the reaction medium, that of the starting compounds and the desired rate of the reaction.

The alkylidene-substituted-1,4-dions derivatives obtained with the process of the present invention can be converted into the corresponding alkyl-substituted derivatives with methods known in the art. These final compounds are used as electron donor in the preparation of Ziegler-Natta heterogeneous catalysts for the polymerization of olefins.

The alkyl-substituted-1,4-dions derivatives can be suitably obtained via the catalytic hydrogenation, this reaction is well known in the art. A review of this kind of reaction can for example be found in Comprehensive Organic Transformation: a guide to functional group preparation by R. C. Larock published by VCH Publishers. Among the various kinds of catalysts which can be used for carrying out this reaction, particularly preferred are the palladium or platinum deposited on carbon, alumina, BaCO₃, CaCO₃ or PtO₂. The content of palladium and platinum for deposited catalyst ranges from 0.5 to 30%, preferably from 1 to 10%. Also usable is the Ni Raney catalyst. The temperature at which this reaction is carried out may range from 0 to 150° C., more typically from 40 to 120° C. The hydrogen pressure is generally higher than the atmospheric pressure and preferably higher than 15 bar. The skilled in the art can easily select, within these ranges, the optimum temperature by taking into account parameters like the boiling temperature of the reaction medium, that of the starting compounds and the like.

Since the 2-alkylidene-1,4 dions derivatives object of the present invention, are intermediates for the preparation of the corresponding alkyl as explained above, even if with the process of the present invention a mixture of isomers of formula (Ia) and (Ib) can be obtained, with the hydrogenation step they become the same compounds and thus the mixture can be used as such without separation of the isomers.

The reaction times for the process of the present invention may be from about 1 min to about 30 hours. More conveniently however, the reaction time is comprised from about 10 min to about 8 hours. In any case, the skilled in the art, can control the state of the reaction by following the techniques known in the art and decide when to stop it.

As explained above this process is very attractive from an industrial standpoint because it allows to obtain the desired product in very good yields and with a minimal work-up. The process of the present invention is also very versatile.

One subclass of compounds obtainable with the process of the invention are diethyl sec-butylidenesuccinate, diethyl cyclopropylidenesuccinate diethyl cyclohexylidenesuccinate, diethyl benzylidenesuccinate, diethyl cyclohexyimethylidenesuccinate, diethyl isobutylidenesuccinate, diethyl isopropylidenesuccinate, diethyl isopentylidenesuccinate and the corresponding products of formula (Ib) and the corresponding compounds esterified with different alkoxy moieties.

When R³ is hydrogen, the 2-alkylidene-1,4-dions derivative obtained with the process of the present invention can be also further substituted on position 3 in a subsequent reaction. The second substitution can be carried out by using the Stobbe reaction, as described for example in EP 01202184.6 with subsequent re-esterification of one acidic group and hydrogenation of the obtained compound.

Thus a further object of the present invention is a process for preparing 2,3-disubstituted-alkylidene-1.4 dions derivatives of formula (IVa), (IVb) or (Ivc) or a mixture thereof:

wherein R¹, R² R⁴ and T² are described above; preferably T² is OR⁴; R⁵ and R⁶ equal to or different from each other, are hydrogen atoms or C₁-C₂₀ hydrocarbon groups; optionally containing heteroatoms belonging to group 13-17 of the periodic table; or R⁵ and R⁶ can join together to form a saturated or unsaturated C₃-C₁₀ ring optionally containing heteroatoms belonging to group 13-17 of the periodic table; with the proviso that R⁵ and R⁶ are not hydrogen at the same time;

comprising the following steps:

-   -   a) reacting a compound of formula (II)         with a compound of formula (Va) or (Vb)         in the presence of at least one equivalent a salts of a base or         a neutral base at a temperature higher than 70° C.;     -   b) treating the compound obtained in step a) with a compound of         formula (VI):         in the presence of a reaction medium and a base; and     -   c) esterifying the product obtained in step b).

Step a) is substantially equal to the process described above.

Step b) is preferably carried out under conditions such that:

-   -   (i) the compound obtained from step a) is used in a molar amount         substantially equal to, or lower than, the amount of compound of         formula (VI);     -   (ii) the base used in step b) is in a molar amount substantially         equal to the compound obtained in step a) and it is selected         from hydrides of formula MeH, where Me is a metal belonging to         group I-II of the periodic table of elements and z is the         valence of the metal and alkoxides of formula R⁵OMe where R⁵ is         a C₁-C₁₅ hydrocarbon group and Me has the meaning given above;         and     -   (iii) the reaction medium comprises an aprotic liquid medium or         a protic liquid medium having a K_(a), measured in water, lower         than that of iso-propyl alcohol (i-PrOH).

According to the present invention by the term “a molar amount substantially equal” is meant an amount which is no more than 10%, preferably 5%, by mol different from the amount of the compound of reference.

The preferred reaction media for step b) are the aprotic diluents and, among them, toluene, ethylbenzene, xylene, dimethylformammide (DMF), N,N-dimethylacetamide, 1-methyl-2-pyrrolidone, diethylether, tetrahydrofurane are particularly preferred. Toluene and DMF are especially preferred and DMF is the most preferred. Among protic solvents tert-butanol is one of the most preferred. According to the present invention, the reaction medium chosen among aprotic liquid medium or a protic liquid medium having a K_(a), measured in water, lower than that of i-PrOH, should be the largely prevailing medium but may be not the only one. This means that small amounts (generally not higher than 10% by volume with respect to the total amount of the diluents of liquids not falling within the above classes can in some cases be present for particular purposes. In particular one of these liquids is preferably ethanol.

The base used in step b) is preferably selected among alkoxides of formula R⁷OMe where R⁶ is a C₁-C₁₅ hydrocarbon group and Me has the meaning given above. Particularly preferred among them are the alkoxides in which R⁶ is a C₁-C₅ alkyl group and Me is Na or K Especially preferred compounds are potassium tert-butoxide, sodium tert-butoxide, potassium ethoxide, sodium ethoxide. As a preferred aspect, such preferred alkoxides are used in combination with the aprotic solvents specified above. In particular the combination of the preferred alkoxides with the aprotic solvents like DMF or toluene is especially preferred.

One class of preferred starting compounds among those of formula (VI) is that in which one of the groups R⁵ or R⁶ is hydrogen and the other group is selected from C₄-C₂₀ hydrocarbon groups, preferably from those not having unsaturation on the carbon atom linked to the carbonyl of formula (VI); particularly preferred are the compounds in which this group is a secondary or tertiary alkyl group. Another class of preferred compounds among those of formula (VI) is that in which both R⁵ and R⁶ are C₁-C₂₀ hydrocarbon groups preferably not having unsaturation on the carbon atom linked to the carbonyl of formula (VI). Among them particularly preferred are the compounds in which R⁵ and R⁶ are C₁-C₈ alkyl groups or R⁵ and R⁶ join together to form cyclic ketones. Examples of suitable ketones are methyl ethyl ketone, methyl n-propyl ketone, cyclobutyl methyl ketone, but-3-enyl methyl-ketone, acetylcyclopropane, diethyl ketone, methoxyacetone, isopropyl methyl ketone, 2-hexanone, 4-methyl-2-pentanone, methyl sec-butyl ketone, methyl tert-butyl ketone, ethyl n-propyl ketone, ethyl isopropyl ketone, isopentyl methyl ketone, 4-methylcyclohexanone, 2-methylcyclohexanone, 3-methylcyclohexanone, 2,2-dimethyl-3-pentanone, 2-heptanone, 3-heptanone, di-n-propyl ketone, , dicyclopropyl ketone, di-isopropyl ketone, neo-pentyl methyl ketone, cyclopentyl methyl ketone, 4-methyl-3-hexanone, 1-methyl-butyl methyl ketone, 3-ethyl-2-pentanone, isopropyl n-propyl ketone, 3-methyl-5-hexanone. The compounds in which both R⁵ and R⁶ are the same and chosen among methyl, ethyl or propyl are preferred. Also preferred are the compounds in which R⁵ and R⁶ are linked together to form cyclic ketones like cyclopentanone, cyclohexanone, or cycloheptanone.

The product of step (b) has a non-esterified carboxylic group formed during this step. In order to transform it into a completely esterified product an esterification step must be carried out which is the step (c) of the process of the invention. The esterification step can be carried out according to any of the many methods known in the art. One of the known methods for obtaining esters includes for example the esterification of a carboxylic acid through the reaction with an alcohol catalyzed by an acid or a base. A comprehensive review of many methods for preparing the esters can be found in Organic Functional Group Preparation, II Edition, Academic Press 1983. The preferred method for carrying out the esterification according to the present invention is the reaction of the product of step (b) with a compound of formula R⁸X where X is halogen and R⁸ is C₁-C₂₀ hydrocarbon group. Preferably, X is selected from Br, Cl and I and R⁷ is a primary C₁-C₈ alkyl group. Particularly preferred R⁸ groups are methyl, ethyl, n-propyl, n-butyl and isobutyl. The use of ethyl bromide is especially preferred. This method has the advantage that the alkylidene substituted product of step (b) can directly be reacted with the compound of formula R⁸X without being first subjected to a preliminary work-up thereby saving time and increasing the yields. The temperature for carrying out step (c) is not critical. It generally ranges from about −30 to 150° C., more typically from −10 to 110° C. The skilled in the art can easily select, within these ranges, the optimum temperature by taking into account parameters like the boiling temperature of the reaction medium, that of the starting compounds and the like.

Preferably in the above described process all steps a), b) and c) are carried out “one pot” i.e. without isolating the intermediate products.

The product of formula (IVa) or (IVb) or (IVc) is subsequently subjected to a hydrogenation step as described above. Thus, since these products are intermediates for the preparation of 2,3-dialkyl-substituted derivatives of succinic and 4-oxo-butanoic acids, even if with the process of the present invention a mixture of isomers of formula (IVa), (IVb) and (IVc) can be obtained, with the hydrogenation step they become the same compounds and thus the mixture can be used as such without separation of the isomers.

The saturated derivatives of succinic and 4-oxo-butanoic acids, object of the present invention, find various applications in the art including the use in the pharmaceutical industry and, as mentioned above, as modifying compounds of Ziegler-Natta polymerization catalysts.

The following examples are given in order to illustrate and not limit the invention.

EXAMPLES

Analytical gas chromatography was performed on Hewlett Packard 6890 GC (Hewlett Packard HP-5, 30 m×0.53 mm×0.88 μm with Packed Inlet and/or Restek Rtx-200, 30 m×0.53 mm×0.50 μm with Cool On-Column Inlet) using flame ionization detector. Final products have been characterized by ¹H NMR (Varian Unity 300 Spectrometer, 300 MHz) and GC/MS (Hewlett Packard 6890 GC with Hewlett Packard 5973 Mass Selective Detector).

Examples 1-3 Synthesis of a Mixture of 2-Isopropylidene-Succinic Acid Diethyl Ester (1) and 2-Isopropenyl-Succinic Acid Diethyl Ester (2) from Maleic Acid Diethyl Ester (3) in Different Solvents

A mixture of potassium carbonate (Aldrich, powder, −325 mesh, not anhydrous, 98+%; 49.5 mmol), an organic sovent (15.0 ml), maleic acid diethyl ester (45.0 mmol), and 2-nitropropane (47.3 mmol) was heated up fast, in 7 min., to a reflux temperature and stirred under reflux until the completion of the reaction according to GC-analysis. All the reactions gave a mixture of two isomeric products 1 and 2 in very high yields without impurities due to maleic acid diethyl ester (3), fumaric acid diethyl ester (4) (product of isomerization of the starting maleic acid diethyl ester which is formed in the course of the reaction), or 2-(1-methyl-1-nitro-ethyl)-succinic acid diethyl ester (5) (intermediate product formed during the reaction). Solvents used, boiling points of the solvents, reaction times, relative amounts of the products 1 and 2, and the combined yields of these products are reported in table 1 below (relative amounts of the products and yields were established by GC; for determination of the yields an internal standard technique was used). TABLE 1 Combined B.P. of Reaction Ratio Yield Ex. Solvent Solvent, ° C. Time, h 1/2 (1 + 2), % 1 N,N- 153 1 92/8  98 Dimethylformamide 2 Diglyme 162 3 89/11 94 3 o-Xylene 143-145 20 88/12 96

Example 4 Synthesis of a Mixture of 2-Isopropylidene-Succinic Acid Diethyl Ester (1) and 2-Isopropenyl-Succinic Acid Diethyl Ester (2) from Fumaric Acid Diethyl Ester (4)

A mixture of potassium carbonate (Aldrich, powder, −325 mesh, not anhydrous, 98+%; 49.5 mmol), N,N-dimethylformamid (15.0 ml), fumaric acid diethyl ester (45.0 mmol), and 2-nitropropane (47.3 mmol) was heated up fast to a reflux temperature and stirred under reflux for 0.5 h to give a 89/11-mixture of two isomeric products 1 and 2 with a combined yield of 92% without impurities due to maleic acid diethyl ester (3), fumaric acid diethyl ester (4), or 2-(1-methyl-1-nitro-ethyl)-succinic acid diethyl ester (5) (relative amounts of the products and yields were established by GC; for determination of the yields an internal standard technique was used).

Example 5 Synthesis of 2.3-Diisopropylidene-Succinic Acid Diethyl Ester (6) from Maleic Acid Diethyl Ester (3) by One-Pot Approach

Potassium carbonate (Aldrich, powder, −325 mesh, not anhydrous, 98+%; 240 mmol), N,N-dimethylformamid (133 ml), maleic acid diethyl ester (400 mmol) and 2-nitropropane (408 mmol) were placed at room temperature in a 1L round bottom 4-neck flask fitted with a mechanical stirrer, a reflux condenser, and a thermocouple. The reaction mixture was brought fast, in 10 min., to a reflux and stirred at reflux for 50 min. After cooling to 75° C. from 150° C., the temperature reached by the mixture in the end of 50 min. of reflux, the reaction mixture was treated with toluene (130 ml) during 8 min. A toluene-water mixture (125 ml) was slowly distilled off during 60 min. while gradually increasing the temperature of the reaction mixture from 75° C. back to 150° C. After cooling to 30° C., the mixture was treated with acetone (432 mmol) added fast in one portion and then with potassium ethoxide (460 mmol) added during 15 min. using a powder addition funnel. The funnel was rinsed with N,N-dimethylformamid (5×10 ml) to transfer all the potassium ethoxide into the reaction flask. After that the reaction mixture was heated to 60° C. and stirred for 30 min. The mixture was then treated with bromoethane (460 mmol) added fast in one portion, warmed up to 80° C., and stirred at 80° C. for 60 min. Following cooling to 60° C., the reaction mixture was treated subsequently with acetone (32.0 mmol) and potassium ethoxide (100 mmol) both added in one portion, stirred for 30 min., then heated up to 80° C., treated at this temperature with bromoethane (216 mmol) added fast in one portion, and stirred at the same temperature for additional 60 min. Upon completion of the reaction, the mixture was cooled to 10° C., quenched with water (333 ml), and then diluted with ether (133 ml). The organic phase was separated and the water phase was extracted with ether (5×100 ml). The combined organic phases were washed three times with water (1×157 ml, 1×100 ml, 1×77 ml), concentrated on a rotary evaporator, and distilled in vacuum (flash distillation) to give 94.4 g of the product (93% yield).

Example 6 Synthesis of 2,3-Diisopropylidene-Succinic Acid Diethyl (6) from Maleic Acid Diethyl Ester (3) by One-Pot Approach

Potassium carbonate (Aldrich, powder, −325 mesh, not anhydrous, 98+%; 240 mmol), N,N-dimethylformamid (133 ml), maleic acid diethyl ester (400 mmol) and 2-nitropropane (408 mmol) were placed at room temperature in a 1L round bottom 4-neck flask fitted with a mechanical stirrer, a reflux condenser, and a thermocouple. The reaction mixture was brought fast, in 8 min., to a reflux and stirred at reflux for 52 min. After cooling to 110° C. from 150° C., the temperature reached by the mixture in the end of 52 min. of reflux, the reaction mixture was treated with toluene (50 ml) added fast in one portion. The reaction flask was then fitted with a 20 ml Dean-Stark receiver, the mixture was heated up to a reflux temperature (˜140° C.) and the water formed during the first stage of the reaction was removed by azeotropic drying total 51 ml of a toluene-water mixture were collected during the azeotropic drying and the subsequent distillation. After cooling to 60° C., the reaction mixture was treated with acetone (432 mmol) added fast in one portion, then with a solution of potassium ethoxide (460 mmol) in a mixture of N,N-dimethylformamide (153 ml) and ethanol (26.7 ml) added dropwise during 10 min., and following the completion of the addition stirred at 60° C. for 30 min. The mixture was then treated with bromoethane (460 mmol) added fast in one portion, heated up from 60° C. to 80° C., and stirred at this temperature for 60 min. After that the reaction mixture was treated with potassium ethoxide (100 mmol) added fast in one portion, stirred for 30 min., then treated with bromoethane (216 mmol) added fast in one portion, and stirred at the same temperature of 80° C. for additional 60 min. Upon completion of the reaction, the mixture was cooled to 10° C., quenched with water (333 ml), and then diluted with ether (133 ml). The organic phase was separated and the water phase was extracted with ether (4×100 ml). The combined organic phases were washed three times with water (1×157 ml, 1×100 ml, 1×77 ml), concentrated on a rotary evaporator, and distilled in vacuum (flash distillation) to give 92.4 g of the product (91% yield).

Comparative Example 1 Synthesis of a Mixture of 2-Isopropylidene-Succinic Acid Diethyl Ester (1) and 2-Isopropenyl-Succinic Acid Diethyl Ester (2) from Maleic Acid Diethyl Ester (3)

A solution of 2-nitropropane (3.90 mmol) and maleic acid diethyl ester (3.00 mmol) in acetonitrile (6.0 ml) was treated with DBU (3.30 mmol) added fast in one portion at room temperature. After stirring for 0.5 h at this temperature, the reaction mixture was evaporated, and then analysed. A 92/8-mixture of two isomeric products 1 and 2 with a combined yield of 81% was obtained accompanied by impurities due to maleic acid diethyl ester (3), fumaric acid diethyl ester (4), and 2-(1-methyl-1-nitro-ethyl)-succinic acid diethyl ester (5); the ratio of the products 1/2/3/4/5 was 89.1/7.6/2.5/0/0.8 (relative amounts of the products and yields were established by GC; for determination of the yields an internal standard technique was used).

Comparative Example 2 Synthesis of a Mixture of 2-Isopropylidene-Succinic Acid Diethyl Ester (1) and 2-Isopropenyl-Succinic Acid Diethyl Ester (2) from Maleic Acid Diethyl Ester (3)

A solution of 2-nitropropane (5.00 mmol) and maleic acid diethyl ester (5.00 mmol) in acetonitrile (20 ml) was treated with DBU (5.00 mmol) added fast in one portion at room temperature. After stirring for 4.5 h, the reaction mixture was treated with additional 2-nitropropane (0.502 mmol) and DBU (0.502 mmol), stirred at room temperature overnight, and then analysed. Reaction times and relative amounts of the products 1, 2, 3, 4, and 5 are reported in the table 2 below. In the end of the reaction a 95/5-mixture of two isomeric products 1 and 2 with a combined yield of 85% was obtained accompanied by impurities due to maleic acid diethyl ester (3), fumaric acid diethyl ester (4), and 2-(1-methyl-1-nitro-ethyl)-succinic acid diethyl ester (5) (relative amounts of the products and yields were established by GC; for determination of the yields an internal standard technique was used). TABLE 2 Reaction Time, h Ratio 1/2/3/4/5 Yield of 1, % Yield of 2, % 10 min 5.8/0.2/41.5/0.2/52.3 — — 3 65.1/1.4/9.4/0.8/23.3 41 1 6 78.3/2.4/5.8/0.6/12.9 59 2 overnight 91.4/4.8/1.2/0.2/2.4 81 4 

1. A process for the preparation of 2-alkylidene-1,4-dions derivatives of formula (Ia) or (Ib) or a mixture of (Ia) and (Ib):

wherein R¹, R² and R³, equal to or different from each other, are hydrogen atoms or C₁-C₂₀ hydrocarbon groups. optionally containing heteroatoms belonging to group 13-17 of the periodic table, or R¹ and R² can join together to form a saturated or unsaturated C₃-C₁₀ ring optionally containing heteroatoms belonging to group 13-17 of the periodic table, with the proviso that when R¹ and R² are both hydrogen atoms, only compounds of formula (Ia) are obtained; T¹ and T², equal to or different from each other, are H, OR⁴, R⁴, NR⁴ ₂, SR⁴ or PR⁴ ₂, or T¹ and T² can be fused in an oxygen atom or a NR⁴ group; R⁴, equal to or different from each other, are a C₁-C₂₀ hydrocarbon group, optionally containing one or more heteroatoms belonging to group 13-17 of the periodic table; said process comprising the step of reacting a compound of formula (II):

with a compound of formula (IIIa) or (IIIb):

in the presence of at least one equivalent with respect to the compound of formula (IIIa) or (IIIb) of a salt of a base or a neutral base at a temperature higher than 70° C.
 2. The process according to claim 1 wherein the salt of a base or a neutral base is: (i) oxides of metals belonging to groups 1-13 of the periodic table; (ii) compounds of formula NR⁹ ₃ wherein R⁹, equal to or different from each other, are hydrogen atoms, or a linear or branched, saturated or unsaturated, C₁-C₁₀ alkyl, C₆-C₂₀aryl, C₇-C₂₀ arylalkyl or C₇-C₂₀ alkylaryl groups, optionally containing O, S, N, P, Si or halogen atoms, or two or more R⁹ form one or more saturated or unsaturated 4 to 7 membered rings, optionally containing O, S, N, P or Si atoms, that can bear substituents and when this ring is aromatic, one R⁹ can also be a bond part of a double bond; (iii) compounds of formula MT_(j) wherein M is a metal of groups 1-12 of the periodic table, or a group (NR⁹ ₄)⁺; T is H, F⁻, OH⁻, HCO3^(−, RO) ⁻ or RC(O)O⁻ wherein R is a linear or branched, saturated or unsaturated C₁-C₂₀-alkyl, C₃-C₂₀-cycloalkyl, C₆-C₂₀-aryl, C₇-C₂₀-alkylaryl or C₇-C₂₀-arylalkyl radical, optionally containing one or more halogen atoms; j is equal to the valence of the metal M or 1 in the case M is (NR⁹ ₄)⁺; or (iv) carbonates of metal M.
 3. The process according to claim 1 wherein R³ is a hydrogen atom, a linear or secondary C₁-C₈ alkyl or a C₅-C₇ cycloalkyl group.
 4. The process according to claim 3 wherein R³ is a hydrogen atom.
 5. The process according to claim 1 wherein R⁴ is a linear or branched C₁-C₂₀ alkyl, C₃-C₁₀ cycloalkyl, C₆-C₁₀ aryl or a C₇-C₁₂ alkylaryl group and T¹ and T² are an OR⁴ group.
 6. The process according to claim 2 wherein M is a metal of groups 1, 2 of the periodic table.
 7. The process according to claim 1 wherein the salt is a carbonate of metal M wherein M is is a metal of groups 1-12 of the periodic table.
 8. The process according to claim 1 wherein said process is carried out at a temperature from 80 to 220° C.
 9. The process according to claim 8 wherein the temperature ranges from 150 to 200° C.
 10. The process according to claim 1 wherein in the compounds of formula (Ia) or (Ib), R² is hydrogen and R¹ is selected from C₄-C₂₀ hydrocarbon groups.
 11. The process according to claim 1 wherein in the compounds of formula (Ia) or (Ib), R¹ and R² are C₁-C₂₀ hydrocarbon groups.
 12. The process according to claim 11 wherein in the compounds of formula (Ia) or (Ib), R¹ and R² are C₁-C₈ alkyl.
 13. A process for preparing 2,3-disubstituted-alkylidene-1.4 dions derivatives of formula (IVa), (IVb) or (IVc) or a mixture thereof:

wherein R¹ and R², equal to or different from each other, are hydrogen atoms or C₁-C₂₀ hydrocarbon groups, optionally containing heteroatoms belonging to group 13-17 of the periodic table, or R¹ and R² can join together to form a saturated or unsaturated C₃-C₁₀ ring, optionally containing heteroatoms belonging to group 13-17 of the periodic table, with the proviso that when R¹ and R² are both hydrogen atoms, only compounds of formula (IVa) or (IVb) are obtained; T² is H, OR⁴, R⁴, NR⁴ ₂, SR⁴ or PR⁴ ₂; R⁴, equal to or different from each other, are a C₁-C₂₀ hydrocarbon group. optionally containing one or more heteroatoms belonging to group 13-17 of the periodic table; R⁵ and R⁶, equal to or different from each other, are hydrogen atoms or C₁-C₂₀ hydrocarbon groups, optionally containing heteroatoms belonging to group 13-17 of the periodic table, or R⁵ and R⁶ can join together to form a saturated or unsaturated C₃-C₁₀ ring, optionally containing heteroatoms belonging to group 13-17 of the periodic table; with the proviso that R⁵ and R⁶ are not hydrogen at the same time; said process comprising the following steps: a) reacting a compound of formula (II)

with a compound of formula (Va) or (Vb)

in the presence of at least one equivalent with respect to the compound of formula (Va) or (Vb) of a salt of a base or a neutral base at a temperature higher than 70° C.; b) treating the compound obtained in step a) with a compound of formula (VI):

in the presence of a reaction medium and a base; and c) esterifying the product obtained in step b).
 14. The process according to claim 13 wherein the salt of a base or a neutral base used in step a) is: (i) oxides of metals belonging to groups 1-13 of the periodic table; (ii) compounds of formula MT_(j) wherein M is a metal of groups 1-12 of the periodic table; T is H, OH³¹ , HCO3³¹ , RO⁻ or RC(O)O⁻ wherein R is a linear or branched, saturated or unsaturated C₁-C₂₀-alkyl, C₃-C₂₀-cycloalkyl, C₆-C₂₀-aryl, C₇-C₂₀-alkylaryl or C₇-C₂₀-arylalkyl radical, optionally containing one or more halogen atoms; and j is equal to the valence of the metal M; (iii) compounds of formula NR⁹ ₃ wherein R⁹, equal to or different from each other, are hydrogen atom, or a linear or branched, saturated or unsaturated, C₁-C₁₀alkyl, C₆-C₂₀aryl, C₇-C₂₀arylalkyl or C₇-C₂₀ alkylaryl groups, optionally containing O, S, N, P, Si or halogen atoms, or two or more R⁹ form one or more C₄-C₇ rings; or (iv) carbonates of metal M.
 15. The process according to claim 13 wherein (i) the compound obtained from step a) is used in a molar amount at most 10% higher than the amount of compound of formula (VI); (ii) the base used in step b) is in a molar amount from 10% higher than to 10% lower than the amount of the compound obtained in step a) and it is selected from hydrides of formula MeH_(z) wherein Me is a metal belonging to groups 1 and 2 of the periodic table of elements and z is the valence of the metal and alkoxides of formula R⁷OMe wherein R⁷ is a C₁-C₁₅ hydrocarbon group; and (iii) the reaction medium comprises an aprotic liquid medium or a protic liquid medium having a K_(a), measured in water, lower than that of iso-propyl alcohol (I-PrOH).
 16. The process according to claim 13 wherein in step c) the product of step (b) is reacted with a compound of formula R⁸X wherein X is halogen and R⁸ is C₁-C₂₀ hydrocarbon group.
 17. The process according to claim 13 wherein step a) is carried out at a temperature from 80 to 220° C.
 18. The process according to claim 17 wherein step a) is carried out at a temperature range from 150 to 200° C.
 19. The process according to claim 13 wherein all steps a), b) and c) are carried out without isolating the intermediate products.
 20. The process according to claim 13 wherein one of the groups R⁵ or R⁶ is hydrogen and the other group is selected from C₄-C₂₀ hydrocarbon groups.
 21. The process according to claim 13 wherein both R⁵ and R⁶ are C₁-C₂₀ hydrocarbon groups.
 22. The process according to claim 3 wherein R³ is methyl, ethyl, isobutyl or cyclohexyl. 